Tsunami are predominantly triggered by strong submarine earthquakes. However, land­slides or a volcanic eruption may also be the reason for a tsunami, which is documented by historical data particularly for the Mediterranean region.

A landslide is often preceded by an earthquake, but this must not necessarily be very strong. However, as many tsunami early warning systems only switch to alarm mode when strong quakes occur, scientists of the German Research Centre for Geosciences (GFZ) in Potsdam are working on the rapid detection of landslides and the changes in sea level caused by them.

A further challenge which must be taken into account by the scientists is the size of the Mediterranean Sea. It is comparatively small, and the tsunami waves can therefore reach every point on the coast quickly, so that the early warning time can, depending on the distance, be extremely short. Furthermore, a warning may have to be issued for several countries, which must also be taken into consideration in the technical development work and training activities.

Mediterranean Sea: wave heights from five to six metres possible

The possible scale of a tsunami in the Mediterranean is quite comparable with the catastro­phic event of December 26, 2004 in the Indian Ocean. “Earthquakes in the Mediterranean region can reach a magnitude of 7.5 to 8, and accordingly wave heights of five to six metres are within the realms of possibility”, says Dr. Jörn Lauterjung from the GFZ. The conse­quences would be disastrous. There is therefore great interest in a tsunami early warning system such as the one in the Indian Ocean.

The GFZ has been supporting since 2005 the Intergovernmental Oceanographic Commission (IOC) of UNESCO, in other words the working group of the United Nations concerned with marine sciences and the associated data and information exchange, in setting up such a system. An initial communication test in August 2011 within the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas (NEAMTWS) was successful. NEAMTWS is one of four worldwide tsunami early warning structures coordinated by the IOC of UNESCO. Comparable systems are in operation in the Pacific, the Indian Ocean and the Caribbean.

"Back in 2005 UNESCO began to identify national institutions in every country bordering the Mediterranean and the adjacent seas, the so-called National Tsunami Warning Focal Points which are responsible for organising the dissemination of information to the competent dis­aster prevention organisations and thus to the population. For several years there have existed national warning centres in France, Portugal and Turkey for example, which monitor seismic activity and sea levels round the clock and trigger an alarm if necessary. So not just one single early warning centre exists in the Mediterranean region, but a federally organised system, which has the advantage that several early warning centres make parallel observa­tions”, continues Lauterjung, explaining the efforts being made to set up a tsunami early warning system in the Mediterranean region.

The GFZ was in charge of setting up a tsunami early warning system for Indonesia. The research centre is also active in the Mediterranean region. "We have naturally contributed our experience from our cooperation with UNESCO. For example, the evaluation system for seismic monitoring (observation of earthquake activity), which was developed by the GFZ for the early warning system in the Indian Ocean, is in operation almost everywhere in the states bordering the Mediterranean. A first model-based hazard and risk analysis for the Mediterranean region based on the many years of work on seismic hazard analysis was also published recently", says Lauterjung.

You can read the articles about tsunami hazard regions in the Mediterranean region here.